A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power.
It is composed of semiconductor material usually with at least three terminals for connection to an
external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current
through another pair of terminals. Because the controlled (output) power can be higher than the
controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged
individually, but many more are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in
modern electronic systems.

Most transistors are made from very pure silicon or germanium, but certain other semiconductor
materials can also be used. A transistor may have only one kind of charge carrier, in a field effect
transistor, or may have two kinds of charge carriers in bipolar junction transistor devices. Many types of
transistors are made to standardized specifications by multiple manufacturers.